Double metal cyanide (DMC) complexes are well known in the art for catalyzing epoxide polymerization. Double metal cyanide (DMC) catalysts for the polyaddition of alkylene oxides to starter compounds, which have active hydrogen atoms, are described, for example, in U.S. Pat. Nos. 3,404,109, 3,829,505, 3,941,849 and 5,158,922. These active catalysts yield polyether polyols that have low unsaturation compared to similar polyols made with basic (KOH) catalysis. The DMC catalysts can be used to make many polymer products, including polyether, polyester, and polyetherester polyols. The polyether polyols obtained with DMC catalysts can be processed to form high-grade polyurethanes (e.g., elastomers, foams, coatings and adhesives).
DMC catalysts are usually prepared by the reaction of an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of an organic complexing ligand such as, for example, an ether. In a typical catalyst preparation, aqueous solutions of zinc chloride (in excess) and potassium hexacyanocobaltate are mixed, and dimethoxyethane (glyme) is subsequently added to the formed suspension. After filtration and washing of the catalyst with aqueous glyme solution, an active catalyst of formula:Zn3[Co(CN)6]2.xZnCl2.yH2O.zglyme is obtained.
Substantially amorphous DMC catalysts having exceptional activity for polymerizing epoxides are described in U.S. Pat. No. 5,470,813. Compared with earlier DMC catalysts, the DMC catalysts described therein possess excellent activity and produce polyether polyols with very low unsaturation. The catalysts of the '813 patent are active enough to allow their use at very low concentrations, often low enough to overcome any need to remove the catalyst from the polyol.
U.S. Pat. No. 4,477,589, issued to van der Hulst et al., teaches an acid modified DMC catalyst prepared initially without organic complexing agent, by the addition of sodium hydroxide to precipitated zinc hexacyanocobaltate to form the intermediate hydroxide salt of the general formula:M1a[M2(CN)b(A)c]d.pM1(OH)q.yH2O This catalytically inactive intermediate is isolated and neutralized by HCl with and without glyme organic complexing agent. Ethers or glymes are the preferred organic activating agent. This patent further teaches the use of Zn and Co in the presence of glyme, HCl, and ZnSO4.
Combs et al., in U.S. Pat. No. 5,783,513, teach a process for making substantially non-crystalline double metal cyanide (DMC) catalysts having improved activity and performance. The process involves using a metal salt having an alkalinity within the range of about 0.2 to about 2.0 wt. % as metal oxide based on the amount of metal salt to prepare the catalyst. This patent further teaches that important polyol properties such as viscosity and unsaturation improve when the alkalinity of the metal salt used to make the DMC catalyst is properly controlled. A hydroxyl ligand is taught by Combs et al.
U.S. Pat. No. 5,627,122, issued to Le-Khac et al., teaches a crystalline DMC complex catalyst containing a DMC compound, an organic complexing agent, and a metal salt. The catalyst contains less than about 0.2 moles of the metal salt per mole of DMC compound; i.e., mole fraction Zn/Co<1.6. Disclosed organic complexing agents include alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitrites, sulfides, and mixtures thereof. With low levels of ZnCl2, these catalysts are very active and produce polyols with very low unsaturation. The metal salt of Le-Khac contains chloride.
Combs, in U.S. Pat. No. 5,952,261, discloses highly active double metal cyanide complex catalysts useful for epoxide polymerization prepared by reacting zinc chloride or other metal salt with potassium hexacyanocobaltate or other metal cyanide salt in the presence of a Group IIA compound such as calcium chloride. The DMC catalyst of Combs '261 is amorphous and contains salts other than hydroxide.
Several patents and applications, in the name of Grosch et al., including U.S. Pat. Nos. 6,303,533, 6,362,126, 6,303,833, and U.S. Pub. Pat. Appl. Nos. 2003/0013604, 2002/0032121, 2002/0006864 generally disclose double-metal cyanide catalysts of the formula M1a [M2 (CN)b (A)c]d. fM1g Xn. h (H2O).eL, where M1 is a metal ion M2 is a metal ion and M1 and M2 are identical or different, A is an anion, X is an anion, L is a water-miscible ligand, a, b, c, d, g and n are selected so as to make the compound electrically neutral, and e denotes the coordination number of the ligand, e and f denote fractions or integers greater than or equal to zero, h denotes a fraction or integer greater than or equal to zero. It appears the metal salt used in making the catalysts disclosed by Grosch must be water-soluble and that metal carboxylates are preferred.
A need exists in the art for a hydroxide containing double metal cyanide (DMC) catalyst and process for production of such a catalyst that does not require use of a water-soluble metal salt. Surprisingly, the crystalline, double metal cyanide hydroxides of the present invention catalyze the polymerization of alkylene oxides whereas the compounds of the art do not.